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There is widespread scientific agreement that the temperature datasets which track rising global temperatures give an accurate view of how the planet is warming. But they are the subject of fierce criticism from climate sceptics, who argue that methodological flaws or scientific conspiracy to massage data mean they cannot be relied upon.

Muller calls the surface temperature record ‘very contentious’ and argues that climate sceptics have raised ‘legitimate concerns’ about the way that temperature data is handled. He recruited a team of statisticians to re-assess temperature data, promising a totally revised approach to understanding the raw data from global temperature stations.

We are publishing for the first time a graph showing preliminary results from this reassessment which show a temperature trend closely in accord with the other three main temperature datasets. The preliminary results are based on an analysis of 2% of the data the BEST project will consider.

The presentation [PDF] containing the graph is from January 2011. Although it’s difficult to draw firm conclusions from this image, Ken Caldeira, a prominent climatologist who donated to BEST, has seen the project’s draft paper. He told US website Climate Progress: “Their preliminary results sit right within the results of NOAA, NASA, and HadCRU, confirming that prior analyses were correct in every way that matters.

“Their results confirm the reality of global warming and support in all essential respects the historical temperature analyses of the NOAA, NASA, and HadCRU. Their analysis supports the view that there is no fire behind the smokescreen put up by climate science deniers.”

A second graphic appears to show the temperature data points used for the preliminary 2% results:

Concerns have been raised around the BEST project after it emerged that the project was granted $150,000 from the Charles G. Koch Charitable Foundation, out of total funding of more than $600,000 – covered in the LA Times today.

Koch Industries, run by billionaire brothers Charles and David, is outspoken in challenging the science of climate change and Charles has donated millions of dollars to think tanks in the United States that have promoted climate scepticism.

Certainly it would be very surprising if a new analysis of the data provided results significantly different to current datasets – which already use a variety of scientific techniques to correct for errors and bias in the raw temperature data, and are regarded by scientists and policymakers as authoritative.

In response to their preliminary findings, the BEST team updated their FAQ to state:

A preliminary analysis of 2% of the Berkeley Earth dataset shows a global temperature trend that goes up and down with global cycles, and does so broadly in sync with the temperature records from other groups such as NOAA, NASA, and Hadley CRU â?¦ the preliminary analysis includes only a very small subset (2%) of randomly chosen data, and does not include any method for correcting for biases such as the urban heat island effect, the time of observation bias, etc. The Berkeley Earth team feels very strongly that no conclusions can yet be drawn from this preliminary analysis.

The presentation containing the graph [PDF] was given in January by Paul Alivisatos, a senior staff member at the Lawrence Berkeley National Laboratory. Muller’s testimony will be available to watch here at 3PM UK time.